1. Field of the Invention
The present invention related to a device for judging a normal operation of a brake system of a vehicle such as an automobile, and more particularly, to such a brake system normal operation judging device that is improved not to make a mistake in the detection of the normal operation of the brake system due to variations of actuation thereof by drivers.
2. Description of the Prior Art
In Japanese Patent Laid-open Publication 5-184007 (1993) there is proposed a device for judging a normal operation of a brake system which judges that the brake system is not normally operating when an output of a brake depression sensor is higher than a predetermined value under an off state of a brake lamp switch.
In the brake systems of vehicles there is generally such a relationship between stroke Sp of a depression of the brake pedal by a driver and pressure Pm generated thereby in the master cylinder as shown in FIG. 8 by a set of up and down solid lines when the brake pedal is depressed at a normal speed, which, however, will change so far as shown by a set of broken up and down lines as the brake depression speed increases. Therefore, when the normal operation of the brake system is judged simply according to whether a normal pattern of brake pedal depression vs. master cylinder pressure is available or not, a mistake can happen in the judgment of the normality of operation of the brake system according to a variation of the manner of depression of the brake pedal by drivers.
In this connection, if the width of a standard range of Sp vs. Pm pattern such as shown in FIG. 3 by a hatching is broadened to give an allowance for changes of the performance pattern due to variations of the actuation of the brake pedal by drivers, there will arise a problem that when the normal operation of the brake system was lost within the allowance range, a certain fault actually occurred in the brake system, even small, continues without being detected.